205. Isomorphic Strings

题目：

Given two strings s and t, determine if they are isomorphic.

Two strings are isomorphic if the characters in s can be replaced to get t.

All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character but a character may map to itself.

For example,
Given "egg", "add", return true.

Given "foo", "bar", return false.

Given "paper", "title", return true.

Note:
You may assume both s and t have the same length.

链接：  http://leetcode.com/problems/isomorphic-strings/

2/24/2017

需要用2个hashmap，aa - > ab是不成立的

public class Solution {
    public boolean isIsomorphic(String s, String t) {
        if (s.length() != t.length()) return false;

        HashMap<Character, Character> h1 = new HashMap<Character, Character>();
        HashMap<Character, Character> h2 = new HashMap<Character, Character>();
        char a, b;

        for (int i = 0; i < s.length(); i++) {
            a = s.charAt(i);
            b = t.charAt(i);
            if (h1.containsKey(a)) {
                if (h1.get(a) != b) return false;
                h1.put(a, b);
            } else {
                h1.put(a, b);
            }
            if (h2.containsKey(b)) {
                if (h2.get(b) != a) return false;
            } else {
                h2.put(b, a);
            }
        }
        return true;

    }
}

别人的好算法可以用bitmap，留给二刷。